The present disclosure relates to pattern forming methods for use in, for example, processes for fabricating semiconductor devices.
With increasing integration of semiconductor integrated circuits and downsizing of semiconductor elements, there has been a demand for acceleration of the development of lithography techniques. At present, pattern formation is performed by photolithography using mercury lamps, KrF excimer lasers, ArF excimer lasers, or the like, as sources of exposure light. Further, the use of F2 laser light having a shorter wavelength of 157 nm was also studied, but is not currently developed because there are still problems in exposure apparatus and resist materials.
Under such circumstances, to further miniaturize patterns by using conventional exposure wavelengths, a technique called double patterning has been recently proposed (see, for example, M. Maenhoudt, J. Versluijs, H. Struyf, J. Van Olmen, and M. Van Hove, “Double Patterning scheme for sub-0.25 k1 single damascene structures at NA=0.75, λ=193 nm,” Proc. SPIE, vol. 5754, p. 1508 (2005)).
With the double patterning technique, a desired mask pattern is divided into two masks which are individually subjected to light exposure, thereby enhancing pattern contrast. The resolution in lithography is defined by k1·λ/NA (where k1 is a process constant, λ is the wavelength of exposure light, and NA is the numerical aperture of exposure apparatus). With the double patterning technique, the enhanced pattern contrast significantly reduces the value of the process constant (k1). Accordingly, the resolution can be greatly increased with a light source using the same wavelength of exposure light.
A pattern forming method using a conventional double patterning technique will be described hereinafter with reference to FIGS. 13A-13D and 14A-14D.
First, a chemically amplified positive resist material having the following composition is prepared.
Base polymer: poly((t-butyl-norbornene-5-2gmethylenecarboxylate)(50 mol %) - (maleic anhydride) (50 mol %))Acid generator: triphenylsulfonium0.05gtrifluoromethanesulfonic acidQuencher: triethanolamine0.002gSolvent: propylene glycol monomethyl ether acetate20g
Next, as shown in FIG. 13A, the chemically amplified resist material is applied on a substrate 1 to form a first resist film 2 with a thickness of 0.12 μm.
Then, as shown in FIG. 13B, the first resist film 2 is irradiated with exposure light which is ArF excimer laser light having an NA of 0.93 through a first mask 3A.
After the pattern exposure, as shown in FIG. 13C, the first resist film 2 is heated with a hot plate at a temperature of 105° C. for 60 seconds. Thereafter, as shown in FIG. 13D, the first resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer, thereby obtaining a first resist pattern 2a made of an unexposed portion of the first resist film 2.
Subsequently, as shown in FIG. 14A, the chemically amplified resist material is applied on the substrate 1 including the first resist pattern 2a to form a second resist film 4 with a thickness of 0.12 μm.
Then, as shown in FIG. 14B, the second resist film 4 is irradiated with exposure light which is ArF excimer laser light having an NA of 0.93 through a second mask 3B.
After the pattern exposure, as shown in FIG. 14C, the second resist film 4 is heated with a hot plate at a temperature of 105° C. for 60 seconds. Thereafter, as shown in FIG. 14D, the second resist film 4 is developed with a 2.38 wt % tetramethylammonium hydroxide developer, thereby obtaining a second resist pattern 4a made of an unexposed portion of the second resist film 4.
In this manner, A process including two lithography steps and an etching step in the double patterning technique has a simple pattern forming process, and thus, is industrially promising.